Medical robotic systems for image-guided interventions require sterilizable precision actuators. Imaging modalities like computed tomography (“CT”) and magnetic resonance (“MR”) imaging impose further limitations on actuator design. It is desirable for the robot and its actuators to be transparent to the imager and to not produce artifacts, noise or distortion in the images. Thus, actuator design is restricted to materials and principles of operation that are compatible with the imaging environment. Together with the requirements for sterilizability and precision control, these restrictions present a challenging design problem.
Over the past 20 years, numerous custom MR-compatible actuators and robots have been reported in the literature. Due to the high strength magnetic field of the MR imager, these actuators cannot contain ferromagnetic materials. Pneumatic actuation has been commonly employed because the working principle does not rely on electromagnetism. Thus, these actuators can be constructed solely from dielectric materials.
Other forms of actuation, in particular piezoelectrics, have been employed in a variety of anatomy-specific MR-compatible robots, including several for neurosurgical procedures. While piezoelectrics offer precise and non-backdrivable actuation, many researchers have reported that the high voltage ultrasonic drivers substantially reduce the signal-to-noise (SNR) ratio of the MR imager, precluding the ability to servo the robot motors while simultaneously acquiring images.
Although piezoelectric actuators can be a viable solution for MR-compatible robots, a low-cost yet customizable actuator that does not require extreme care in the design and shielding of drive electronics is desirable. Furthermore, both pneumatic and piezoelectric robots for MRI-guided interventions as reported in the literature have been limited to linear needle trajectories.